1) Field of the Invention
The present invention relates to a technology for recording and reproducing apparatuses, and more particularly, to a recording and reproducing apparatus that can be used for run-length-limited code at a high encoding rate satisfying a plurality of conditions of constraint regarding a string of successive zeros.
2) Description of the Related Art
Conventionally, a recording and reproducing apparatus having an encoder for encoding an information bit string to an encoded bit string and a decoder for decoding the encoded bit string to an information bit string has been widely used as a recording and reproducing apparatus for magnetic disks, optical disks, magneto-optical disks, etc. In such a recording and reproducing apparatus, for data recording, error correcting code (ECC) encoding is first performed and then run-length-limited (RLL) encoding is performed. For data reproduction, RLL decoding is first performed and then ECC decoding is performed. With such a configuration, errors tend to be propagated at the time of RLL decoding, and will exceed the limitation of error correction in ECC decoding. For example, Japanese Patent Laid-Open Publication No. 2003-68024 discloses a recording and reproducing apparatus of a conventional technology, in which, for data recording, ECC encoding is first performed and then RLL encoding is performed and, for data reproduction, RLL decoding is first performed and then ECC decoding is performed.
In a permutation scheme, the order of RLL encoding and ECC encoding and the order of RLL decoding and ECC decoding are each reversed. That is, error correction is performed with ECC decoding, and then RLL decoding is performed. Therefore, RLL code at a high encoding rate can be applied, thereby improving a signal-to-noise ratio. Also, in the permutation scheme, since RLL code at a high encoding rate is used, a replacement scheme with a small amount of calculation and a small circuit size is expected to be applied. A conventional technology regarding such a replacement scheme is disclosed in, for example, A. J. van Wijingaarden and K. A. Schouhamer Immink, “Construction of Constrained Codes employing Sequence Replacement Techniques”, Proc. IEEE ISIT97, Ulm, Germany, pp. 144, Jun. 29, 1997.
However, in the conventional replacement scheme, although a G condition of constraint that limits a maximum number of bits of successive zeros (hereinafter, “0-run”) is satisfied, an I condition of constraint that limits a maximum number of bits of 0-run for every two bits is not satisfied. Also, a process between code bit strings has such a problem as that the I condition of constraint is not satisfied, although the G condition of constraint is satisfied.